After watching videos of Marcus and Lukas during their manic episodes, Oscar could not see anything wrong with it (other than the peculiar behavior by Marcus and Oscar).
One video showed Marcus sitting on the bed and then suddenly snapping to the side and screaming at their grandfather how he is not useless while throwing things in one corner. Video clearly shows that Marcus is the only person in the room.
The second video is Marcus staring into the television and then his sight moved to the side and he started talking to their father. Again, no one else is in the room.
They watched a video showing Lukas: suddenly he would shrink into a corner and cover himself with a bedsheet while saying weakly: "Take whatever you want and leave, just don't kill me…"